The objectives of this investigation are to determine the ultrastructural and biochemical events in the formation, storage and release of insulin from beta cells of different species including Man and the factors which control these processes. A perifusion system has been developed for the study of the pattern of insulin secretion of isolated islets of the rat, lizard and man. This system will be used to continue the studies on the role of the microtubular system in beta cell secretion and the mechanism by which cytochalasin B produces enhancement of glucose-induced insulin secretion. A technique has been developed for long-term monolayer culture of islet cells which will be used for scanning electronmicroscopic and cinephotomicrographic studies on insulin secretion. Studies will be continued on the mechanism of action of alloxan in inhibiting glucose-induced insulin secretion in perifused islets and the effect of alloxan and cytochalasin B on hexose transport and metabolism in isolated islets. Studies will be continued on the isolation and in vitro perifusion of human islets in order to delineate the normal mechanism of secretion in Man and, in the future, to search for possible defects in this mechanism in the beta cells of diabetic subjects.